Among applications of a WLAN system, application scenarios such as a sensor, a smart grid, a smart meter, and a mobile data bypass are gaining increasingly widespread attention. In applications of this type, a large number of stations (Stations, STAs for short) may exist in a basic service set (Basic Service Set, BSS for short). In some application scenarios, a BSS may support as many as 6000 STAs. If a large number of STAs need to be associated with an access point (Access Point, AP for short) at the same time in the system, because an association process for each STA requires several channel contentions, a severe collision problem causes congestion in the system, and it may take a very long time to complete the association processes for all the STAs. For example, when the following cases occur, the AP may encounter the scenario where a large number of STAs need to be associated:
1) The loss of power on a transmission line causes a large number of smart grid devices, sensors, or smart meter devices to restart.
2) The reset of a power supply of the AP causes all devices to lose the association with the AP.
Because a large number of STAs such as a sensor and smart meter work at a relatively low rate, for example, 100 kbps, and lengths of frames of information exchanged in the association processes are relatively large, the possibility of collision further increases when a hidden node exists in the system. If a large number of STAs need to be associated at the same time in the BSS, it takes tens of minutes to several hours or even longer to complete simultaneous association processes for hundreds to thousands of STAs. When service types such as a health monitoring sensor and a fire alarm sensor which have relatively high requirements for a time delay exist in the system, the excessively long association time cannot satisfy the service demand.